As stated in the title of this descriptive specification, the present invention relates to a process for reduction of the common mode current for power line communications equipment, which has the object of reducing the level of common mode signal in order to satisfy the standards of different countries on power line communications equipment, all of which without having to reduce the injected power, which would worsen the coverage and the efficiency of the communications system.
In general, the invention is applicable to any electric circuit in which the common mode current needs to be reduced and more particularly in electric circuits used in telecommunications equipment which use the mains network as transmission medium.
Defined below are some terms which are used in this document. Let a signal source be formed from an electric generator, a circuit via which the generated current flows and an additional circuit suitable for passing current coming from the generator and connected to the circuit in some way. Common mode current is defined as being that current which flows through the conductor and returns via the circuit or the source.
Moreover, common mode choke is described as being that device capable of attenuating or reducing the level of the common mode current in an electric circuit. Power line communications equipment is likewise defined as the type of communication by means of electrical defined as the type of communication by means of electrical signals that use the low, medium or high tension electrical mains network as communications channel.
In the majority of electrical systems, common mode currents need to be attenuated due to their actual functioning, with the aim of reducing the electromagnetic interference with other devices.
The state of the art already contains devices for reducing common mode currents, as an example of which one can cite switched power supply sources which use common mode filters for reducing their conducted and radiated electromagnetic emissions [which can be found in many different documents such as AN 15 on POWER INTEGRATIONS]. Another example is communications by means of Ethernet cable, fitted with common mode chokes for reducing their conducted and radiated emission levels in the corresponding frequency band.
There currently do not exist devices for reducing in any effective way common mode levels in power line communications systems, and the devices existing and used in other applications are of no use for this type of communications on account of their limitations regarding working voltages and attenuations in differential mode. Moreover, in order for the reduction in common mode current to be effective, both the way in which the common mode, choke is constructed and its location in the communications circuit are of overriding importance.